Eh, I can kinda see it. It depends on your definitions of words. People have been muddying the waters with what "open source" means anyway. I have known it to mean code released under an open source license. Other people use it to mean programs where the source is available regardless of license. I would use "source available" to describe that, but some people strongly disagree with my definitions.

If I write a program, then obfuscate it and then release the obfuscated code under an open source license, would you consider it open source(I would)? That's kind of the case here, they are releasing the model weights under an open source license.

Personally, I think it's fine to shorten it to "open source model" instead of "a model with the weights released under an open source license". What I would object to is releasing model weights under a restrictive license and calling that open source.